Relative Humidity Probe Depth

[mwoody]

I've got a project with 5.5 inch thick elevated concrete slabs on 2 inch composite metal deck. To what depth do the humidity probes get installed? 40% of 5.5 inches? 40% of 3.5 inches? By the time the flooring gets installed the building is essentially finished with ceiling components and makes it difficult to determine the high and lows of the poured concrete deck.